In conventional automobiles, trucks and like motor vehicles, a wide variety of accessory equipment is typically provided, including for example power-assisted steering and braking units, air conditioning units, engine cooling arrangements, and electrical generators or alternators for providing power for various electrically-operated equipment. The driving members for these various accessories are conventionally driven rotatably directly from the crankshaft of the vehicle engine. Accordingly, the driving members are subject to a widely varying rotational driving input speed during the course of the ordinary operation of the vehicle, the rotary input speed from the crankshaft typically varying several thousand revolutions per minute. Because ordinary vehicle driving conditions require frequent periods of engine operation at low, idling speeds thereof, most of these accessory units are necessarily designed for operation at full capacity and/or optimum efficiency at low or idling engine speeds. Therefore, at all greater engine speeds in excess of idling speed, a progressively greater than necessary rotational input speed is transmitted from the engine crankshaft to these accessory units, whereby these units are caused to be operated at high levels of inefficiency, with attendant decreases in available motive engine horsepower and fuel economy, throughout the periods of operation of the vehicle at speeds other than idling speed. In addition to the aforementioned disadvantages of inefficiency, the varying rotational input speeds to these accessories create correspondingly varying physical and/or electrical strains thereon which initially requires special engineering of the accessories to withstand such strains and ultimately may contribute to or cause the premature failure of the accessories.
The foregoing shortcomings of conventional arrangements for powering vehicle accessory units are generally recognized in U.S. Pat. No. 3,958,419, wherein there is disclosed an apparatus for driving automobile accessory units at respective optimum constant speeds using an expansion engine powered by the flow of induction air to the main automobile engine. Conceptually, the invention described in this patent is considered to provide significant advantages over the conventional accessory driving arrangement described above, but the invention is not known to have achieved any reasonable degree of commercial recognition or success.
In contrast, the present invention provides an efficient hydraulic fluid power transmission of a relatively simple and operable construction adapted for receiving a variable speed rotary input force and transmitting a relatively substantially constant speed rotary output force, for use in conjunction with a vehicle engine for drivingly transmitting the varying crankshaft speed thereof at respective constant output speeds to equipment accessory thereto, as well as for use in widely varying other embodiments wherein it is desirable to provide a constant output speed from a varying input speed.